1. Field of the Invention
The present invention relates to a measuring technique of sound characteristics in a sound space, such as a reverberation characteristic, and an automatic sound field correcting technique by using the measuring technique.
2. Description of Related Art
For an audio system having a plurality of speakers to provide a high quality sound space, it is required to automatically create an appropriate sound space with much presence. In other words, it is required for the audio system to automatically correct sound field characteristics because it is quite difficult for a listener to appropriately adjust the phase characteristic, the frequency characteristic, the sound pressure level and the like of sound reproduced by a plurality of speakers by manually manipulating the audio system by himself to obtain appropriate sound space.
So far, as this kind of automatic sound field correcting system, there is known a system disclosed in Japanese Patent Application Laid-open under No. 2002-330499. In this system, for each signal transmission path corresponding to plural channels, a test signal outputted from a speaker is collected, and a frequency characteristic thereof is analyzed. Then, by setting coefficients of an equalizer provided on the signal transmission path, each signal transmission path is adjusted to have a desired frequency characteristic. As the test signal, a pink noise is used, for example.
The above-mentioned measurement of the frequency characteristic is performed by outputting the test signal which is comparatively long in view of time. For example, in order to measure a characteristic of a frequency band of about 20 Hz, the test signal is outputted during a time period equal to or larger than 50 ms (msec), corresponding to one period of the 20 Hz test signal, and is collected by a microphone. Thereby, the frequency characteristic is measured. Therefore, it is difficult to obtain an instantaneous sound characteristic in a certain sound field or a sound characteristic in quite short time width (e.g., about 5 ms). Particularly, when the frequency band subjected to measurement is a low-frequency band, it is necessary to perform the measurement during the period including one period of the test signal of the low-frequency at the minimum, as described above. Therefore, it is difficult to measure the instantaneous sound characteristic or the sound characteristic in quite the short time width, in such the low-frequency band.
However, there is sometimes required such the instantaneous sound characteristic or the sound characteristic in quite the short time width. For example, in correction of the sound characteristic by the above-mentioned automatic sound field correcting system, when the sound characteristic is desired to be corrected on the basis of only a sound characteristic in a specific period comparatively short in view of time after outputting the test signal, it is necessary to measure the sound characteristic only in that short time period.